I. Field of the Invention
The present invention relates to acoustic systems used in fluidic environments. More particularly, the present invention relates to the multi-element transducer arrays of the type typically used in sonar systems.
II. Description of the Related Technology
Multi-element acoustic transducer arrays are useful in a wide variety of sonar system applications, including those used for underwater current profiling and velocity measurement. Additional details regarding the construction and operation of an acoustic Doppler current profiling (ADCP) system are contained in Reissue U.S. Pat. No. 35,535, "Broadband Acoustic Doppler Current Profiler" issued Jun. 17, 1997, incorporated by reference herein in its entirety. Prior art transducer array configurations (such as the Janus configuration of FIG. 1) were designed so that two acoustic beams emitted by two oppositely-positioned transducers were coplanar. Each acoustic beam did not lie in a distinct geometric plane.
In a concave housing plate (e.g., the vessel mount configuration) which is common in the art, the acoustic beams emitted from the transducers cross over after emission at or about the focal region of the plate. The acoustic beams are emitted in a closely packed manner which causes them to interact after emission. For current profiling, the sound energy in the acoustic beams is reflected off of particles in the water and Doppler shift of the echo is used to calculate water velocity. Any particles present within the focal region are ensonified from all directions of emission. The multi-ensonification effect on these particles produces multiple echoes at each transducer. This results in multiple Doppler shift measurements which may be undesirable. To avoid multiple measurements, current profiling does not commence in the vessel mount configuration until after the beam cross over takes place, i.e., beyond the focal region.
An acoustic transducer array configuration is needed which minimizes the acoustic coupling between each beam of the array, thereby increasing its signal-to-noise ratio and overall performance. Such a configuration would also obviate the requirement that profiling be conducted only at ranges greater than the "cross over" distance of the beams in concave configurations.